The invention relates to a gantry system for adjusting and aligning an ion beam onto a target, according to the preamble of claim 1.
A gantry system of that kind is known from U.S. Pat. No. 4,870,287. In the case of the known gantry system, the ion beam is supplied to the gantry system in the horizontally arranged gantry rotation axis and is firstly deflected from the gantry rotation axis by means of magnetic optics.
The ion beam is then guided parallel to the gantry rotation axis by means of magnetic optics and, from that direction parallel to the gantry rotation axis, is finally deflected into a radial direction with respect to the gantry rotation axis. The target is generally arranged at the point of intersection of the radially directed ion beam with the gantry rotation axis. That point of intersection is defined as the isocentre.
Consequently, on one full revolution of the gantry about the gantry rotation axis, the ion beam can be aligned onto the target in a plane perpendicular to the gantry rotation axis and adjusted to angles between 0 and 3600xc2x0.
Besides the gantry, the gantry system comprises a target carrier system having a rotatable target carrier. The carrier rotation axis of the target carrier is arranged in the isocentre in a vertical direction with respect to the gantry rotation axis. Consequently, the gantry system, which comprises at least one gantry and one target carrier system, can so adjust and align an ion beam that a target arranged in the isocentre can be irradiated from a freely determinable angle in space. In the of a gantry system of that kind, it is necessary for the final deflection magnet of the gantry to deflect the ion beam by 90xc2x0, which is why a gantry of that kind is also referred to as a 90xc2x0 gantry.
In the case of the 90xc2x0 gantry known from the publication U.S. Pat. No. 4,870,287, therefore, the ion beam is, on leaving the gantry in the direction of the gantry rotation axis, perpendicular to the gantry rotation axis. An angle xcex1 of gantry rotation is defined between the plane in which the ion beam is guided through the gantry and the horizontal plane of the space in which the gantry rotation axis is located. A horizontal position of the gantry accordingly corresponds to either the angle xcex1=0 or the angle xcex1=180xc2x0 when the gantry is in the horizontal plane and consequently the ion beam is guided in the gantry in that horizontal plane. The uppermost position of the gantry in the vertical direction accordingly corresponds to the angle xcex1=90xc2x0 and the lowest position of the gantry has an angle of xcex1=270xc2x0.
A treatment angle xcex3 is defined between the horizontal plane of the space and the direction in which the ion beam enters a target volume. An effective treatment angle is defined between a frontal plane of a patient and the direction in which the ion beam enters a target volume. For a patient in a lying position, which is usual, the treatment angle and the effective treatment angle are identical.
In the 90xc2x0 gantry system known from the publication U.S. Pat. No. 4,870,287, the target carrier is in the form of a table rotatable about a vertical axis and having a longitudinal axis and a transverse axis. An angle xcex2 of target carrier rotation is defined between the longitudinal axis of the target carrier table and the gantry rotation axis. By virtue of the rotatability of the target carrier about a vertical axis, the angle xcex2 can have values between 0xc2x0 and 360xc2x0. For a prespecified treatment angle xcex3, which is dependent upon the gantry rotation angle xcex1, it is furthermore possible for a specific entry channel for tumour irradiation to be selected by adjusting the angle , of carrier rotation. By virtue of the adjustability of the angle xcex2, which is associated with the target carrier rotation, and the adjustability of the angle xcex1, which is associated with the gantry rotation, it is possible in a conventional system, wherein the ion beam is deflected by the final deflection magnet in a radial direction with respect to the gantry rotation axis, for the target volume fixed on the target carrier to be aligned for any entry channel for the purpose of tumour treatment.
The 90xc2x0 gantry system known from the publication U.S. Pat. No. 4,870,287 has the disadvantage that the final deflection magnet of the gantry must deflect the ion beam through at least 90xc2x0 in order to make possible all treatment angles xcex2 in a gantry system having a target carrier system. The large deflection angle of the final deflection magnet necessitates, depending upon the mass number of the ions to be deflected, a large radius or a high magnetic field strength. Associated with that is the disadvantage that, on the one hand, a gantry has hitherto been successfully constructed only for ions having the smallest mass number, that is to say for protons; for ions having a higher mass number of between 4 and 16 the final deflection magnet inflates the scale and mass of the gantry to such an extent, because of the heavy ions having a mass number higher than a proton, that a gantry system is no longer appropriate for clinical use.
In order to reduce the mass and volume of a gantry for ions that are heavier than protons, proposals exist for the use of super-conducting materials for the exciting coils of the deflection magnets. Although the masses to be rotated and the volume of the gantry would be reduced as a result, the costs for cooling the super-conducting materials would make the gantry system considerably more expensive, especially as 360xc2x0 rotation is extremely problematic for a cooling system using liquid helium or liquid nitrogen for modern super-conducting materials.
A further proposal, presented in the Japanese publication Journal of the Japanese Society for Therapeutic Radiology and Oncology, vol. 9, suppl. 2, November 1997 as part of the Proceedings of the XXVII PTCOG Meeting by M. Pavlovic under the title xe2x80x9cGSI Studies of a Gantry for Heavy Ion Cancer Therapyxe2x80x9d, enables the mass and volume of the gantry to be reduced by changing the degree of deflection of the final deflection magnet from, formerly, 90xc2x0 to 60xc2x0. That solution has the disadvantage that it is possible to achieve a treatment angle xcex3 of only from 0xc2x0 to 60xc2x0 by means of a so-called 60xc2x0 gantry of that kind in conjunction with the conventional target carrier system. Consequently, it is no longer possible to achieve treatment angles xcex3 of between greater than 60xc2x0 and 90xc2x0 by means of a gantry system of that kind, which has a deflection angle of 60xc2x0 for the final deflection magnet.
The problem of the invention is to provide, by means of a gantry having a reduced deflection angle of the final deflection magnet, a gantry system according to the preamble of claim 1 that does not require super-conducting materials for the magnetic optics and that, despite reducing the deflection angle of the final deflection magnet to below 90xc2x0, allows an ion beam to be adjusted and aligned onto a target from a freely determinable effective treatment angle. The problem of the invention is furthermore to provide a method for irradiating a target volume and adjusting and aligning an ion beam for treatment of a tumour using the gantry system according to the invention.
That problem is solved by the features of the subject matter of claims 1 and 60.
For that purpose, the final deflection magnet so deflects the ion beam that it intersects the gantry rotation axis in the isocentre at an angle of between greater than or equal to 45xc2x0 and less than 90xc2x0, so that the ion beam describes a surface of a cone on rotation of the gantry through a full revolution about the gantry rotation axis, and the target carrier system has a target carrier for two positions, which are perpendicular to one another in a vertical plane, the carrier rotation axis of which target carrier can be brought into the isocentre of the gantry system. Such a solution has the advantage that the target carrier has to be fixable only in two specific positions and, in both positions, which are perpendicular to one another in a vertical plane, has to be rotatable about a vertically aligned carrier rotation axis. A significant advantage of this gantry system is that even angles that are less than 90xc2x0 and preferably less than 60xc2x0 and that therefore advantageously make possible an extremely low gantry volume and extremely small dimensions for the diameter of a gantry can be achieved by means of the gantry system according to the invention. Such a compact gantry system does not require expensive auxiliary equipment for cooling super-conducting materials. A further advantage of such a gantry having conventional magnetic optics is that it is now also possible for ion beams of ions that are heavier than protons, having mass numbers of between 4 and 16, to be adjusted and aligned for any freely determinable effective treatment angle by means of a gantry system that is suitable for clinical conditions.
In order to irradiate a target volume with an optimum dose distribution, there is preferably provided, in the case of the gantry system according to the invention, a deflection means for the ion beam in order to scan the target volume layer by layer therewith. The ion beam is preferably guided in the gantry, from the coupling-in point of the ion beam into the gantry rotation axis to the deflection of the ion beam in the final deflection magnet of the gantry system, by first deflecting the ion beam away from the gantry rotation axis using a 38xc2x0 deflection magnet and by bringing it into a direction parallel to the gantry rotation axis using a second 38xc2x0 deflection magnet. In that parallel direction, the ion beam passes through two scanner magnets, which deflect the ion beam in two directions oriented perpendicular to one another (horizontal and vertical with respect to the ion beam) and orthogonal to the ion beam, so that scanning of a surface of the target volume is advantageously made possible after the scan-deflected ion beam has passed through the final deflection magnet.
The preferred positioning of the scanning system upstream of the final deflection magnet accordingly reduces the gantry radius considerably and requires, however, an enlarged aperture in order to allow a large treatment area. That preferred arrangement of deflection magnet and scanning systems exhibits a high degree of ion-optical flexibility. The ion beam in the isocentre can therefore be modified advantageously from 2 to 16 mm diameter and the magnetic optics of the gantry are always achromatic.
In a preferred embodiment of the invention, the final deflection magnet so deflects the ion beam that the gantry rotation axis is intersected in the isocentre at an angle of greater than or equal to 45xc2x0 and less than 60xc2x0. The deflection angles of below 60xc2x0 especially show the enormous advantages of the present invention in that, on the one hand, the gantry dimensions are minimised and, on the other hand, the gantry system in the combination of the preferred embodiment of the gantry with the target carrier system according to the invention ensures that an ion beam can be adjusted and aligned onto a target from a freely determinable effective treatment angle.
In a preferred embodiment of the invention, the target carrier system has a revolving platform, which is rotatable about a vertical revolving platform axis. Arranged on that revolving platform are two target carriers in two positions, the positions being perpendicular to one another in a vertical plane. Each of the two target carriers is rotatable about a vertical carrier rotation axis.
That preferred target carrier system allows for a patient to be arranged in either a lying or a sitting position on the target carrier, depending upon the effective treatment angle. For medical reasons, the effective treatment angle must be a freely determinable angle in the patient co-ordinate system in order to ensure as far as possible optimum scanning of the target volume by the ion beam.
Optimisation of the ion beam dose distribution in the target volume or in a volume element of the target is substantially dependent upon the structure of the healthy tissue on top of the tumour volume, through which healthy tissue radiation has to pass. The medical determination of the effective treatment angle and entry channel accordingly has to take appropriate account of tissue cavities and densifications of tissue, for example in the case of bone tissue, as well as the location of critical organs in the vicinity of the tumour. In that regard, a freely determinable effective treatment angle, which is made possible by the gantry system according to the invention, is a great advantage for clinical treatment.
The vertical carrier rotation axes of the two positions of the target carriers can preferably be brought alternately into the isocentre of the gantry system by means of a revolving platform as a result of rotation of the revolving platform about its revolving platform axis. This preferred embodiment is associated with the advantage that the patient can be positioned in one of the two positions on the appropriate target carrier and can then be brought on the target carrier into the isocentre of the gantry system by means of the revolving platform. The gantry can then be adjusted to the previously determined angle a and the target carrier in the selected position can be adjusted to the predetermined angle xcex2 by means of a rotary movement about the vertical carrier rotation axis. After those three adjustments, the target volume can then be scanned with the scan-deflected ion beam.
In a further preferred embodiment of the invention, the target carrier system has two separate delivery rails, on each of which there is arranged one target carrier of the two positions, the delivery rails being capable of laterally displacing, from different directions in each case, either of the target carriers with its rotation axis into the isocentre alternately. That system has the advantage that the patient can be positioned and prepared on the selected target carrier outside the isocentre and can then be brought into the isocentre by displacement on the delivery rails. In the isocentre, the target volume can be scanned if in the meantime the gantry rotation angle xcex1 has been adjusted by rotation of the gantry and xcex2 has been adjusted by rotation of the target carrier.
In another preferred embodiment, the target carrier system has a universal robot system, which arranges the target carrier in two positions and arranges the vertical carrier rotation axes in the isocentre. Such multi-axis robot systems enable a rotatable target carrier to be arranged in different positions in the isocentre and consequently replace the two target carriers of disparate construction that are otherwise necessary as well as any delivery rails or revolving platforms. Such a universal robot system can, for this preferred application, be greatly simplified, especially because only two positions located perpendicular to one another in the vertical plane are required for the rotatable target carrier.
The method for irradiating a tumour from a freely determinable effective treatment angle by means of a gantry system is characterised by the following method steps:
a) determining the most advantageous effective treatment angle and the most advantageous entry channel with respect to the location and size of a tumour in healthy tissue and with the requirement for minimum exposure of the surrounding tissue to radiation together with optimum distribution of an ion beam dose for the tumour tissue to be irradiated,
b) selecting, from two positions located perpendicular to one another in a vertical plane, the target carrier position required for the determined effective treatment angle,
c) bringing the carrier rotation axis of the suitable target carrier position into the isocentre of the gantry system,
d) aligning and adjusting the target carrier by rotation of the target carrier about its vertical carrier rotation axis in respect of the most advantageous angle,
e) aligning and adjusting the gantry by rotation of the gantry about its horizontal gantry rotation axis in respect of the most advantageous angle,
f) spatially scanning the entire tumour volume, by means of the ion beam, from the effective treatment angle.
This method has the advantage that, by means of the combination of a gantry system that is limited to treatment angles xcex3 and a target carrier system that delivers the target to the gantry isocentre in two positions located perpendicular to one another in a vertical plane, any freely determinable effective treatment angle can be adjusted for irradiating the tumour volume so that a target can be irradiated with ions without restricting the effective treatment angle. In this context it is immaterial whether the angle xcex1 is first adjusted by means of the gantry and then the angle xcex2 is adjusted by means of the target carrier or whether the reverse order is selected.
It is merely of significance that for effective treatment angles of from 0 to 90xc2x0 minus xcex only one position and therefore, preferably, one of the target carriers can be used and for angles between 90xc2x0 minus xcex and the deflection angle xcex of the final deflection magnet both positions of the target carrier can be utilised and for effective treatment angles between the deflection angle of the final deflection magnet and 90xc2x0 the other of the two positions for the target carrier can be employed. The fundamental advantage of this method is consequently that, despite the final deflection magnet having a restricted deflection angle, the tumour to be treated can be treated with an ion beam from any freely determinable direction and therefore the medically optimal irradiation direction can be achieved by means of a gantry system of reduced mass, volume and cost.